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Humans blamed for 'unequivocal' global warming in landmark report

Oceans are taking the brunt of climate changes - absorbing CO2, warming, and taking many more tonnes of water from melting ice caps. Photo: Reuters

Scientists at the United Nations have implored governments to act to do more to mitigate the potentially devastating effects of climate change and increased global warming, a challenge they described as the "greatest of our time."

Today the UN's Intergovernmental Panel on Climate Change (IPCC) released its fifth assessment of the state of the world's climate, and said categorically that they believe human activity is now the biggest threat facing the planet.

To begin to limit the impact of these changes, "substantial and sustained" cuts in carbon dioxide are needed

Global sea level has already risen by 19cm in the last century, and scientists are 90% sure that this rate will increase further

Sea tide lines are rising as warming glaciers and ice sheets melt into oceans - which are warming, and therefore spreading into shore

Greenland and Antarctic ice sheets are losing mass as glaciers continue to shrink

Global temperatures are likely to rise by more than 1.5 degrees, and could rise by 4 degrees, should emissions continue to increase

In the report summary, the authors said global warming is "unequivocal" and they are 95% certain that the majority of the warming, including the rapid acceleration since the 1950s, is down to human activity.

Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system

Climate change deniers have said the slowing of the pace of temperature warming (one of the multiple indicators of climate change) after fast gains in the 1980s and 1990s is a sign that global warming may not be as urgent as previously believed.

The report will face extra scrutiny after the IPCC made errors in its 2007 report, including an exaggeration of the melt rate of Himalayan glaciers. An outside review of the IPCC found that the mistake did not affect its main conclusions.

Stressing the report was about evidence, not "ideology," the United Nations Environment Programme's executive director said:

Observations of changes in the climate system are based on multiple lines of independent evidence.

Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased.